U.S. Pat. No. 5,537,533 describes tools and techniques for remote mirroring of digital data from a primary network server to a remote network server. A system according to that patent includes a primary data transfer unit with a primary server interface and a primary link interface, and a remote data transfer unit with a remote link interface and a remote server interface. The primary link interface includes a spoof packet generator capable of generating a pre-acknowledgement for the primary network server. That is, the system has a “smart buffer” which gives the primary server a pre-acknowledgement or “spoof” after mirrored data has been stored on a nonvolatile buffer in the primary link interface and before an acknowledgement arrives indicating that the mirrored data has been stored by the remote server.
MiraLink Corporation of Salt Lake City, Utah is the owner of U.S. Pat. No. 5,537,533. MiraLink has made commercially available for more than one year before the date of the present application an Off-SiteServer product (OFF-SITESERVER is a mark of MiraLink). The Off-SiteServer product includes technology to remotely mirror the disks of a Novell NetWare server to another server at a geographically remote location through a low bandwidth telecommunications link (NETWARF is a mark of Novell, Inc.).
Remote mirroring of data from a primary network server to a remote replacement network server using data mirroring is a powerful and efficient method to back up data. Remote mirroring creates a copy of data at a safe distance from the original data and does so substantially concurrently with the storage of the original data. The remotely stored data can be available almost immediately after a disaster if it was copied to a “warm” remote network server, that is, a remote server which can be up and running as the new primary server within minutes of the actual or simulated disaster.
In a typical installation, use of the Off-SiteServer product involves a pair of Off-SiteServer boxes; one is a local box and the other is a remote box. The Off-SiteServer boxes are configured with specialized hardware and with firmware and/or other software, generally as described in U.S. Pat. No. 5,537,533. A proprietary serial line connects the local NetWare server to one of these boxes. The NetWare server itself uses a Vinca card (VINCA is a mark of Vinca Corporation). This card is driven by a NetWare Loadable Module (“NLM”) that intercepts disk-driver requests, and sends data down the serial line to the local Off-SiteServer box.
The local Off-SiteServer box has a 4 Gigabyte nonvolatile buffer, such as an IDE disk drive. Data is pre-acknowledged into this Off-SiteServer buffer. As far as the operating system of the local server is concerned a second “mirrored” write has occurred locally. In reality, the Off-SiteServer product has received this data from the NLM and stored it on the local buffer. The local Off-SiteServer box stores sector and track (or block level) data changes until it can safely send them to the remote Off-SiteServer box at the remote location. The buffer in the local Off-SiteServer box is also “smart” in that it stores any data above what the telecommunications link can handle locally. This data is stored in the local Off-SiteServer box until the remote Off-SiteServer box has successfully written to the remote secondary server and sent back an acknowledgement to the local (primary) Off-SiteServer box. When this acknowledgement is received the local Off-SiteServer box frees the space in the local nonvolatile buffer that is occupied by the successfully transmitted piece of sector/track/block data.
The Off-SiteServer product uses a V.35 interface for data output at the local (primary) site. V.35 is a serial telecommunications standard that connects to a Channel Service Unit/Data Service Unit (“CSU/DSU”), which in turn interfaces with the telecommunications link. The remote (secondary) location has a second CSU/DSU that relays the sector/track/block information to the V.35 input interface of the remote secondary Off-SiteServer box. The secondary Off-SiteServer box outputs this sector/track/block data through the proprietary serial connection using a serial cable connected to another Vinca card in the secondary (remote) server. The remote server's data mirroring and system software then writes this sector/track/block information to the remote server's disk drive and the write is acknowledged back to the local Off-SiteServer box. This system is capable of handling about 300 megabytes of change data in an hour.
The Off-SiteServer product is intelligent enough to sense if there is a decrease or increase in bandwidth and/or if the telecommunications link has gone down. During link downtime periods, the Off-SiteServer box can store data changes from the server in the local nonvolatile smart buffer. When the link is active again, the Off-SiteServer product starts transmitting automatically. The Off-SiteServer product can change its bandwidth output on the fly as bandwidth becomes more or less available. All of the transmissions described above also incorporate standard software checksum error detection and correction, and/or hardware error correcting code (“ECC”) error handling.
In case of a disk or server failure on the local (primary) NetWare server, a secondary (remote) server attached to a remote (secondary) Off-SiteServer box in the manner just described has a complete mirrored disk copy of all the data on the local (primary) server. This remote backup copy can be restored back to the local (primary) server. This secondary remote server can also stand in for the local primary server in the event of disaster. Such a secondary restoration and/or stand-in can be executed relatively quickly with a simple set of command lines.
In short, the Off-SiteServer product and other remote data mirroring technologies provide valuable fault-tolerance and disaster recovery capabilities, both to mission-critical data and in other contexts. Nonetheless, these existing approaches have unnecessarily limited flexibility.
For instance, the Off-SiteServer product requires a specific version of hardware and software from Vinca Corporation. This required version of the Vinca product does not support any operating system/file system platform other than the Novell NetWare platform. The hardware component of the necessary Vinca package also does not work with newer, faster servers and larger disk volumes.
The original Off-SiteServer product was also designed to connect one local server to one remote server. Only a single server can mirror to a remote server at a given time. Multiple servers at different locations cannot readily mirror to a single remote site. Likewise, if an enterprise has multiple local servers running different operating systems and/or file systems, each server running a separate platform must be mirrored to a matching remote server.
In addition, the original Off-SiteServer product requires an NLM on the local server, and it was designed to use private dedicated telecommunications links. Conventional mirroring also requires a remote server in order to keep mirrored information in a bootable format at the remote location.
These limitations and others were noted in the parent application Ser. No. 09/438,184. The present application provides additional tools and techniques for remote data mirroring, in order to take advantage of technologies discussed in the parent application as well as other advancements.